migration: VMSTATE_FD

Define VMSTATE_FD for declaring a file descriptor field in a
VMStateDescription.

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Link: https://lore.kernel.org/r/1736967650-129648-15-git-send-email-steven.sistare@oracle.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>

include/migration/vmstate.h

@@ -230,6 +230,7 @@ extern const VMStateInfo vmstate_info_uint8;
 extern const VMStateInfo vmstate_info_uint16;
 extern const VMStateInfo vmstate_info_uint32;
 extern const VMStateInfo vmstate_info_uint64;
+extern const VMStateInfo vmstate_info_fd;
 
 /** Put this in the stream when migrating a null pointer.*/
 #define VMS_NULLPTR_MARKER (0x30U) /* '0' */
@@ -902,6 +903,9 @@ extern const VMStateInfo vmstate_info_qlist;
 #define VMSTATE_UINT64_V(_f, _s, _v)                                  \
     VMSTATE_SINGLE(_f, _s, _v, vmstate_info_uint64, uint64_t)
 
+#define VMSTATE_FD_V(_f, _s, _v)                                  \
+    VMSTATE_SINGLE(_f, _s, _v, vmstate_info_fd, int32_t)
+
 #ifdef CONFIG_LINUX
 
 #define VMSTATE_U8_V(_f, _s, _v)                                   \
@@ -936,6 +940,9 @@ extern const VMStateInfo vmstate_info_qlist;
 #define VMSTATE_UINT64(_f, _s)                                        \
     VMSTATE_UINT64_V(_f, _s, 0)
 
+#define VMSTATE_FD(_f, _s)                                            \
+    VMSTATE_FD_V(_f, _s, 0)
+
 #ifdef CONFIG_LINUX
 
 #define VMSTATE_U8(_f, _s)                                         \
@@ -1009,6 +1016,8 @@ extern const VMStateInfo vmstate_info_qlist;
 #define VMSTATE_UINT64_TEST(_f, _s, _t)                                  \
     VMSTATE_SINGLE_TEST(_f, _s, _t, 0, vmstate_info_uint64, uint64_t)
 
+#define VMSTATE_FD_TEST(_f, _s, _t)                                            \
+    VMSTATE_SINGLE_TEST(_f, _s, _t, 0, vmstate_info_fd, int32_t)
 
 #define VMSTATE_TIMER_PTR_TEST(_f, _s, _test)                             \
     VMSTATE_POINTER_TEST(_f, _s, _test, vmstate_info_timer, QEMUTimer *)

migration/vmstate-types.c

@@ -314,6 +314,29 @@ const VMStateInfo vmstate_info_uint64 = {
     .put  = put_uint64,
 };
 
+/* File descriptor communicated via SCM_RIGHTS */
+
+static int get_fd(QEMUFile *f, void *pv, size_t size,
+                  const VMStateField *field)
+{
+    int32_t *v = pv;
+    *v = qemu_file_get_fd(f);
+    return 0;
+}
+
+static int put_fd(QEMUFile *f, void *pv, size_t size,
+                  const VMStateField *field, JSONWriter *vmdesc)
+{
+    int32_t *v = pv;
+    return qemu_file_put_fd(f, *v);
+}
+
+const VMStateInfo vmstate_info_fd = {
+    .name = "fd",
+    .get  = get_fd,
+    .put  = put_fd,
+};
+
 static int get_nullptr(QEMUFile *f, void *pv, size_t size,
                        const VMStateField *field)